CVE-2026-6517 | Mattermost Desktop App versions <=6.1 5.5.13.0 fail to restr… | CVSS 6.3 MEDIUM

Description

Mattermost Desktop App versions <=6.1 5.5.13.0 fail to restrict the allow list of domains to which NTLM credentials were forwarded to in the Mattermost Desktop App which allows any user on a server without the image proxy enabled to intercept other users credentials via embedding an image that routes to an external web server. Mattermost Advisory ID: MMSA-2026-00651

Metadata

CVE ID: CVE-2026-6517
State: PUBLISHED
Assigner: Mattermost
Reserved: 2026-04-17 14:25 UTC
Published: 2026-06-15 13:55 UTC
Last updated: 2026-06-15 16:00 UTC
Primary CWE: CWE-522
CWE-522: Insufficiently Protected Credentials
Vendor / Product: Mattermost / Mattermost
Sources: cve.org · NVD

Severity & Metrics

6.3 MEDIUM CVSS 3.1

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N

SSVC — CISA Coordinator

Exploitation: none
Automatable: no
Tech. Impact: partial

Affected products (1)

Vendor	Product	Platform	Versions
Mattermost	Mattermost	—	0 ≤ 5.5.13, 6.2.0, 5.13.6.0

Weakness (CWE)

CWE	Source	Description
CWE-522	cna	CWE-522: Insufficiently Protected Credentials

CVSS scores (1)

Score	Severity	Version	Source	Vector
6.3	MEDIUM	3.1	cna	CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N

References (1)

MMSA-2026-00651 https://mattermost.com/security-updates